Question

In the xy-plane, the graph of the function f(x) = x^2 + bx + 4 does not intersect the x-axis. Which of the following must be true about b?


A.−8 ≤ b < −4
B. b = −4
C. −4 < b < 4
D.b = 4
E. 4 < b ≤ 8

Answer 1

I am not looking for someone to fully teach this to me, I learned this before its just coming back from summer my brain isn't clicking with any of the math stuff I need it too and I just need someone to help me remember it please

Answer 2

@Squirrels

Answer 3

I just need to know the process to go about solving this not the actual answer

Answer 4

Are you familiar with the quadratic formula?
\[x=\frac{ -b \pm \sqrt{b^2-4ac} }{ 2a }\]
This is the quadratic form.
\[ax^2+bx+c=0\]

Answer 5

yes and you can plug in the quadratic form to the formula to solve for x

Answer 6

so your saying I can plug that in to the quadratic formula to solve for x?

Answer 7

@Squirrels

Answer 8

Well this is just to find both cases. In this case we are trying to find 'b'

Answer 9

yeah your trying to find b so how will the quadratic formula help me find b? @Squirrels

Answer 10

Well we already know 'a' is 1. So lets plug that in real quick.
\[y=\frac{ -b \pm \sqrt{b^2-4\times1\times4} }{ 2\times1 }\]
\[y=\frac{ -b \pm \sqrt{b^2-16} }{ 2 }\]

Answer 11

And we know 'c' is 4. Forgot to mention that #sry

Answer 12

we don't do anything about the x squared next to the a in the original problem?

Answer 13

Sorry, again that equation does not equal y it equals 'x'. Its 2:30 am. Forgive me errors </3

And yea we did do something to that x^2, see how there no number next to it? That means it equals '1'.

Answer 14

okay so to solve for b we just set x =1?

so x= -b +/- (b-4)/2 ?( sorry Its really poorly written since I don't know how to write it in the actual equation like you did) @Squirrels

Answer 15

also squirrels if I wanted to look up more questions in this general area of math, like on a website what topic would this be under?

Answer 16

On second thought i might have done that part wrong. I forgot the rest, or at least I am unsure #SoSry

Answer 17

that's fine but can you atleast tell me like what topic this is under so I can look it up online on how to solve problems like these? @Squirrels

Answer 18

Im checking

Answer 19

thank you

Answer 20

@Squirrels did you find anything?

Answer 21

All I can find is this, not too much of a reliable source but i think it will work. check out the second answer https://answers.yahoo.com/question/index?qid=20130622144516AAwnIj5

Answer 22

thanks but also is there a general topic for these types of questions so I can look it up on kahn academy @Squirrels

Answer 23

Oh yeaaa, khan academy... I keep forgetting about that site. I'm sorry. A good tip is to tag those users with green or purple on their name. Most of them are much more experienced.

Answer 24

alright thankyou

Answer 25

@shamim could you help me with this problem?

Answer 26

ya i wanna try to solve it

Answer 27

alright thankyou, and could you show the steps as you solve it please. @shamim

Answer 28

sorry

Answer 29

@shamim can you not solve it? if not do you know where to look to find examples like this?